1. Field of the Invention
The present invention relates generally to wireless communications, and more particularly to a method and apparatus for automatically adjusting the amount of gain or loss in a communication system in which signals are relayed between a master system unit and a remote unit in order to compensate for varied environments.
2. Description of the Related Art
Modern communications systems are an important part of our society today. One such communications system is a wireless cellular communication system. In wireless cellular communication systems, communications between users are conducted through one or more base stations. The term forward link is used to refer to communications from a base station to a subscriber station, and the term reverse link is used to refer to communications from a subscriber station to a base station. A subscriber station is the device that is used by an individual who subscribes to a communication provider for communication services. For example, a person who uses a conventional cellular telephone is a subscriber to the cellular telephone services provided by a cellular telephone service provider, such as Leap Wireless International Inc.
By transmitting information on a reverse link to a base station, a subscriber may communicate with people at other locations through any one of a number of communications systems, including conventional telephones, cellular telephones, or the Internet. The base station receives the information (voice or data) from the first subscriber station and routes the information to a Base Station Controller (BSC). The base station controller routes the information to a Mobile Switching Controller (MSC). The base station serving the subscriber stations sends the information back to the subscriber on the forward link.
As a subscriber station moves about a wireless cellular communication system, the quality of the forward and reverse links to transmit data will vary. In particular, a user of a subscriber station may move inside a building or enter an area in which signals are blocked, such as a tunnel or valley. When the user does so, the subscriber station may not be able to operate due to the low energy level in the signal that is available to and from the subscriber station.
One solution to this problem is to establish a relay station that can receive signals from a base station and relay (i.e., retransmit) those signals to the user's subscriber station. However, in complex structures, such as buildings having several floors and corridors, a simple relay station is not effective. Accordingly, another approach is to place a master system unit at a location from which signals to and from a base station can be transmitted and received, respectively. Signals are then communicated over a wire line to a remote unit. The remote unit transmits information received from the base station via the master system unit to subscriber stations within an area into which signals transmitted directly from the base cannot easily be received. Likewise, the remote unit receives information from subscriber stations within the area. The remote unit then communicates the information received from the subscriber stations over wire lines to the master system unit. The master system unit communicates the information over the air to the base station.
One significant problem with such a configuration of the master system unit and remote units is that the design and installation of such a system is expensive and complex. One of the reasons for this is that the distances between the master system unit and the remote units are not known until the installation site has been selected. Therefore, each system must be customized to the site to account for the particular physical relationship between the master system unit and the remote units. Furthermore, while it is preferable to have as many remote units coupled to one master unit as possible in order to reduce the cost of the system, there is a trade-off between the distance that a remote unit can be from the master system unit, and the number of remote units that can be connected to the master system unit. That is, the more remote units the master system unit has to drive, the shorter the cable has to be between each remote unit and the master system unit. One way to resolve this problem is to add gain (i.e., using amplifiers to boost the signal) at the master system unit and the remote units to increase the length of the wire line between the master system unit and the remote unit. However, by increasing the gain, signals will over-drive the inputs to closer remote units. Therefore, it is difficult to provide off-the-shelf integrated equipment that can be used in the wide range of physical sites in which such equipment is required to operate.
Accordingly, there is a need for a system that allows a master system unit to drive remote units at a greater distance while accommodating a broad range of physical configurations.